We have been studying macrophage activation by bacterial endotoxin through Toll-like receptors or by cytokines and chemokines through their receptors in relation to inflammatory responses and inflammatory diseases. Production of proinflammatory cytokines, such as TNF and IL-1, reactive nitrogen products such as nitric oxide, and matrix metalloproteases, such as MMP-2 and MMP-9, and MMP-14, have all been found to be associated with macrophage activation and inflammatory disease processes.

One project I have been involved with investigated why human monocytes/macrophages failed to produce nitric oxide (NO), in the same manner as murine cells when stimulated with bacterial endotoxin. NO is a reactive nitrogen intermediate, produced by the enzyme inducible nitric oxide synthase (iNOS) important in innate immune responses against various pathogens including bacteria, protozoa, and certain viruses. The apparent inability of human cells to produce NO was due to the lack of iNOS mRNA transcription and this was related to the absence of protein kinase C-eta (PKC-eta) expression by the human cells. Transfection of the PKC-eta gene into human cells reversed this and the cells then became sensitive to bacterial endotoxin, produced mRNA for iNOS and released NO. Studies were undertaken to see if similar results could be found clinically in an inflammatory disease. It was shown, using monocytes obtained from patients with mild arthritis, that circulating peripheral blood monocytes first expressed PKC-eta, and then in severe disease they express both PKC-eta and iNOS, and released NO into the circulation, thus supporting the earlier findings above. Further work is underway investigating the cytokine regulation of the PKC-eta and iNOS phenotypes in patients with rheumatoid arthritis.

A second project in development is the synthesis and screening of triterpenes based on the natural product Triptolide, a compound isolated for the Chinese herbal medicine called the Thunder-God vine. We have shown that these compounds have immunoregulatory activity and inhibit bacterial endotoxin induced proinflammatory cytokines, iNOS, NO and MMP production in macrophage cell lines. They have therapeutic potential in diseases such as inflammatory arthritis.

Nitric oxide in bone and joint physiology and pathophysiology. TNQ Pham, P Rahman and VJ Richardson, 2009, 123-156, in Perspectives on NO in Physiology and Pathology. Editors VJ Richardson and AV Wallace. Published by Transworld Research Network.